A quartz heating element comprises an elongate, coiled resistance heater wire housed inside a hollow, heat-radiating quartz tube. The particular heating appliance shown in the '001 patent has two vertically-oriented quartz tubes arranged side-by-side, the ends of which are received in pairs of pockets in respective upper and lower ceramic insulators. Cold wires or rods welded to the ends of the heater wires and extending through the ceramic insulators provide connection to a source of household electrical power. One end of each heating element is connected to a suitable power switch operable so that only one or else both of the heating elements can be energized in order to provide different heating levels.
Many models of portable space heaters have horizontally-oriented quartz heating elements. In operation of the heating elements, the resistance heater wires become soft and elongated. In use, the heated resistance wires in horizontally-oriented quartz heating elements relax and may partly rest harmlessly against the quartz tubes. During use of a vertically-oriented quartz heating element, the turns of the coils of the softened resistance wires lower through the tube and some of the coil turns rest on lower coil turns. In time, some of the insulating coating on the resistance wires may deteriorate due to abrasion and electrical shorts between coil turns may occur, causing localized parts of the resistance wires to become hotter than other parts. In consequence, it is not uncommon for a vertically-oriented resistance wire to fail to operate with advantage after a few heating seasons. Replacement of worn out heating elements is possible but requires the services of a skilled technician with proper tools, knowledge and replacement components. In practice, heating elements are probably rarely replaced so that the useful life of a portable space heater employing them is limited to the useful life of the heating elements.
Portable radiant space heaters are now being provided with guards or grills that are pivotally mounted along one edge thereof to the heater housing and releasably connected along its opposite edge to the housing. This construction enables a user to easily pivot the grill to enable access to the reflector for cleaning purposes. The Underwriters' Laboratories, Inc. (UL) requires that the connection of a releasable guard or grill cannot be manually disconnected without the use of a tool, and portable space heaters are now being provided that require the use of a screw driver to disconnect the grill connection. It is reasonable to expect that the person who disconnects the grill will proceed cautiously to clean the reflector. However, there are occasions, such as will be described below, when it would be desirable to better ensure that the heater is not connected to an electrical energy source when the grill is pivoted out-of-the-way.